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Thread: Don't throw out faulty Evohome HR92s

  1. #1
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    Default Don't throw out faulty Evohome HR92s

    I was amazed to see that faulty Evohome HR92 TRVs do successfully sell on eBay, listed as "for parts or not working". I just sold one which is dead after a battery leak.

    So, if you prefer not to add to landfill, there is a way to avoid it if you are willing to write the eBay listing and then post it. Mine sold for £10, which isn't much, but it perhaps makes it worth the effort.

    (There's a market for most broken electronics. I got £100 for a TV that was zapped by a lightning strike!)

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    Just curious, which batteries do you use? I've got duracells in mine but even those have leaked on occasion in different devices.

    I wonder if there is something that can be done in an attempt to prevent a leak, maybe moving them around into different heads so they are not always in the same place, assuming it's due to specific environmental conditions (maybe if they are too warm or too cold?).

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    Quote Originally Posted by therealfronty View Post
    Just curious, which batteries do you use? I've got duracells in mine but even those have leaked on occasion in different devices.

    I wonder if there is something that can be done in an attempt to prevent a leak, maybe moving them around into different heads so they are not always in the same place, assuming it's due to specific environmental conditions (maybe if they are too warm or too cold?).
    I've has two types leak. Duracell Pro and Amazon (supposedly leakproof). I'm switching to using rechargeable, as they very rarely leak.

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    I've been using GP Ultra or Varta Alkaline's in mine for over 5 years - never had any leak or even show any signs of leaking.

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    Automated Home Jr Member DerekWilliamsUK's Avatar
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    +1 for GP Ultra. Never seen any leaks.

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    Quote Originally Posted by DBMandrake View Post
    I've been using GP Ultra or Varta Alkaline's in mine for over 5 years - never had any leak or even show any signs of leaking.
    Which is what I would have said, six months ago. Alkalines don't leak frequently, but it only takes once to write off a £60 TRV.

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    Automated Home Sr Member philchillbill's Avatar
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    Rechargeable (even low self-discharge NiMH) will need charging every 3 months. I had 2450mAH Eneloops in use and they drove me mad. Also, the battery clip is crap in the HR92 so you will eventually write off a HR92 due to regular changes, methinks. I switched to Energizer Lithium instead. Just sayin'...

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    I really don't see the attraction of using NiMH in the HR92. The only real benefit is from a waste reduction perspective, in every other way they're vastly inferior in this application.

    Aside from the high (by alkaline standards) self discharge rate of even "low self-discharge" NiMH which results in most of the energy being wasted in self discharge instead of actually powering the device, (in this application) I don't think most people realise just how much lower energy density NiMH is compared to Alkaline let alone Lithium.

    Typical capacity of AA size NiMH is only around 1200 - 2000 mAh, while Alkaline is up around 3000mAh, so 50% better than the very best NiMH. That ratio doesn't tell the full story though - due to the very low intermittent current drain of the HR92 and the high self discharge of NiMH the performance ratio is much higher - I get about 18 months from Alkaline and while I haven't actually tried NiMH I'd say it would be only 3-6 months depending on self discharge rate.

    Where Alkaline are a bit weak is usable capacity under high load, like cameras, toy cars etc - in a high discharge application Alkaline are not optimal, there you would use NiMH or Lithium, however the HR92 is not a high discharge application for an AA size cell even when the motor is turning let alone during the 99% of the time that the device is sleeping in low power mode. (And the bursts of higher current drain from the motor have sufficient "rest" time between them)

    Lithium will outlast Alkaline in an HR92 but not by the same ratio of the price increase. With Lithium you're paying for the convenience of changing the cells a bit less often. Good if they're installed in your elderly parents house who live 50 miles away and are technophobes who need you to look after their HR92's, but not the best value for money on your own system.

    Personally I couldn't be bothered with having to charge 18 AA NiMH batteries twice a year. Alkaline are cheap, long lasting and well suited to this sort of sporadic low current use. Lithium are also a good choice with slightly different price/performance trade-offs.

    The point about excessive handling of the flimsy battery terminals in the HR92 is also a good one - I only change my batteries every 18 months and even then I always have to re-tension the battery terminals because they have sagged and stopped making good contact.
    Last edited by DBMandrake; 29th May 2021 at 11:17 PM.

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    I started changing my batteries for Eneloops about 18 months ago as the alkalines that I had in there died. I did this for 2 reasons. Firstly, I thought it was wasteful to be throwing away all those batteries every 18 months. Secondly, I had a terrible habit of trying to eek as much capacity as possible out of them before I changed them. On more than a few occasions this resulted in the batteries dying whilst the HR92 was trying to operate, inevitably leading to a hot room. With the rechargeables, I now just change them as soon as I get a battery warning.

    I have to say that I havenít noticed a huge increase in frequency of having to change the batteries. Iíve never actually recorded when Iíve changed one to see how long they last, but Iím certainly getting longer than 3-6 months and I would estimate closer to a year.

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    Quote Originally Posted by philchillbill View Post
    Rechargeable (even low self-discharge NiMH) will need charging every 3 months. I had 2450mAH Eneloops in use and they drove me mad. Also, the battery clip is crap in the HR92 so you will eventually write off a HR92 due to regular changes, methinks. I switched to Energizer Lithium instead. Just sayin'...
    Some good points. I had a look at Energizer Lithium and the Ultimate are guaranteed against leakage. If they leak, they replace your device. I think this might be the way to go.
    Edit: they are only guaranteed in the US, not in UK. However, the Alkaline Max are guaranteed in the UK, so I think I would go for them.
    Last edited by IvanOpinion; 2nd June 2021 at 06:05 PM.

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